The present invention relates an apparatus for use in an electron microscope and to the detection of electron images by converting them into light images and transferring them onto an electronic light-imaging device.
Electron microscopes use a beam of accelerated electrons which pass through or are deflected by a sample to provide an electron image and/or diffraction pattern of the sample. To provide a record of these images and/or diffraction patterns, the electrons have been converted into light images using scintillator materials (e.g., phosphors), and the light images and/or patterns are then captured by an imaging sensor. A transfer optic, typically one or more optical lenses or a fiber optic plate, transfers the light image to the imaging sensor. While photographic film and cameras have long been used to capture such light images and/or diffraction patterns, charge-coupled devices (CCD) of the type originally developed for astronomy to read light images into a computer have found increasing use in this field. Such CCD cameras offer excellent resolution, sensitivity, linearity, up to 2,048.times.2,048 pixels, are reusable, and make the image available for viewing within seconds of recording.
A conductive medium is typically coated onto the entrance surface of the scintillator to prevent the buildup of electrical charges and also to prevent the entry of light from external sources. When the transfer optic is a fiber optic plate, the scintillator is typically glued onto the fiber optic plate, and the plate is then coupled with optical coupling oil to the imaging sensor.
The resolution of prior art devices is limited by a number of factors including the extent to which light generated at a particular spot on the scintillator is imaged onto a single pixel at the imaging sensor. Current image coupling devices lose resolution due to leakage of light sideways, either in the scintillator, the transfer optic, or both.
Accordingly, the need still exists in the art for an apparatus which will improve the ultimate resolution of image sensors used to record images from electron microscopes.